World Trade Center Dust

Settled Dust Aerosol From the Pulverized Towers

Within one minute of the North Tower's collapse,
the mammoth cloud of thick dust engulfed most of the southern end
of Manhattan.
See other photographs
of the dust clouds.

When the South Tower and then the North Tower exploded
they each produced
vast clouds of dust
that first so attenuated the sunlight on the streets below that witnesses
described a pitch-black environment.
They then settled, covering virtually every surface
with fine, penetrating dust.
The dust permeated the insides of buildings,
and contaminated air conditioning systems,
necessitating lengthy decontamination procedures.

The dust was present everywhere around Ground Zero,
but settled in thicker accumulations in the downwind directions
south and east of the complex.
The dust settled to a depth of 3 inches in locations
as far as six blocks from the World Trade Center.
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Apparently the dust contained a significant proportion of the
towers' constituents, such as their concrete, glass, and gypsum.
Photographs of Ground Zero
show piles of shattered steel and aluminum cladding,
but show virtually no signs of the tens of thousands of tons of
concrete that constituted the 4-inch-thick
floor slabs
of each of the towers' 110 floors.
This observation, combined with the documented extent of the dust,
suggests that the vast majority of that concrete was pulverized
into fine dust.

The Lioy et. al. Dust Study

A score of scientists conducted detailed analysis of selected dust samples
in order to determine the exposure of nearby residents and workers
to toxic contaminants.
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The study performed inorganic and organic analysis on dust samples
collected from three locations.
The inorganic analysis identified radionuclides, ions, and asbestos;
and the organic analysis identified numerous dangerous types of compounds,
including:
polycyclic aromatic hydrocarbons (PAHs);
polychlorinated biphenyls, dibenzodioxins, and dibenzofurans;
phthalate esters;
and brominated diphenyl ethers.
Unfortunately for those affected,
the study's discovery of carcinogenic materials was not disclosed
until a summary of the findings were published in
EHP in November of 2001.
By that time, the
worst exposures had already occurred.

The study was based entirely on dust samples collected
from just three locations:

A building on Cortlandt Street, one block east of the WTC.

An automobile on Cherry Street, about 0.7 km east of the WTC.

An automobile on Market Street, about 0.7 km east of the WTC.

All three locations were sheltered, rain on September 15
having washed away dust in exposed locations.
The study used three principal methods to determine
physical and chemical characteristics of the dust.

Whereas the study was undertaken to assess the risks of the
dust to human health,
we examine the results with a different objective:
to see what evidence they provide about how the buildings were destroyed.
We asked the following questions:

What fraction of the dust was concrete,
and what was the average particle size?

What levels of radioisotopes were measured
and were those levels consistent with known sources in the
buildings and crashed aircraft?

What levels of sulfur were measured,
given the evidence of steel corrosion through sulfidation
documented in the
limited metallurgical examination
of the FEMA Report's Appendix C ?

Were explosive residues detected?

The dust samples from the study, taken from sheltered areas,
were light and fluffy.
They were apparently not representative of the thick fallout
that settled on the streets.

Unfortunately, despite the detail of the study,
it fails to provide satisfying answers to these questions.
The report does not quantify what proportion of the dust was
pulverized concrete,
though it does note that the samples were very alkaline.
It notes that significant portions of the dust were glass fibers
and cellulose fibers, and that the samples were fluffy.
Thus, it appears that the samples were not representative of the dust
that settled in open areas in the immediate aftermath of the attack.
Being from sheltered areas, their samples were likely biased greatly
in favor of lightweight fibrous debris,
which would tend to stay aloft much longer than powdered concrete.

In regard to radioisotopes, the report is rather cryptic.
It states:

We analyzed approximately 50 peaks based on statistical significance
(counting/lack of interferences). These included thorium, uranium,
actinium series, and primordial radionuclides

However, it fails to quantify how the levels of these
radionuclides compare to background levels.

The report makes several mentions of sulfur,
indicating that many glass and cement particles
in a fibrous form contained sulfur.
It also mentions that the three samples contained around 40,000 ng/g
of sulfides.
Interestingly, it states that
X-ray analyses showed large signals for iron,
but fails to quantify the proportion of iron,
omitting it from the table giving concentrations of elements.

Finally, the scientists did not broach the issue
of whether the dust showed evidence of explosive residues.
Their report does not appear to have sufficient detail to use it
as a basis for drawing any conclusions about the question of explosives.
All their disclosures of the dust composition are partial,
addressing questions about the levels of heavy metals and
toxic hydrocarbons, but failing to provide even complete
compositional analysis of elements.

The USGS Study

A study by the US Geological Survey (USGS) provides some analytical
detail missing from the above study.
It lists the elemental composition of a number of dust samples
collected from outdoor and indoor locations.
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The following table summarizes the percentages by weight of
the more abundant elements in samples for which sulfur was measured.

sample

element: percentage by weight

Si

Ca

Mg

S

Fe

Al

WTC 01-02

21.20

15.01

3.11

1.33

4.13

4.13

WTC 01-03

26.30

9.58

2.23

0.87

2.16

2.75

WTC 01-14

15.30

17.65

2.83

4.32

1.87

2.86

WTC 01-15

13.60

18.58

2.64

5.40

1.87

2.59

WTC 01-16

17.00

13.36

1.79

3.68

1.92

2.27

WTC 01-21

12.80

18.94

2.68

5.10

1.49

2.73

WTC 01-22

17.00

16.80

2.77

3.70

2.78

2.78

WTC 01-25

13.20

20.37

3.29

4.03

1.33

3.28

WTC 01-27

15.20

19.51

3.04

4.29

1.72

3.05

WTC 01-28

13.80

19.65

2.83

4.56

1.80

2.95

Gypsum, the primary constituent of most wallboard,
has the formula CaSO4-2(H20),
and is 18.62% sulfur and 23.38% calcium by weight.
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Gypsum is also about 5% of portland cement,
the binder used in most concrete and constituting.
Since aggregate constitutes between
70% and 80% of most concrete, gypsum might account for
1% to 1.5% of the concrete in the towers.
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The DELTA Group Study

A group of scientists at UC Davis,
the DELTA Group (Detection and Evaluation of Long-range Transport of Aerosols),
performed what they described as the
"most thorough analysis yet" of Ground Zero dust and smoke
in May of 2002.
The study was based on the analysis of air samples from
a rooftop air monitor about one mile north-northeast of Ground Zero.
The group noted that very fine particles were found at levels
not previously found in ambient air,
and that the particles included metals such as vanadium.
They also noted that particles of concrete and glass were
coated with combustion products.
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They identified high levels of coarse particles, above, which included
powdered concrete and glass with a coating of combustion products,
in size range of 5 to 12 micrometers diameter. Very fine particles
were found at levels not previously seen in ambient air samples.

Studies by Ryan, Jones, et. al.

By 2008, if not earlier,
the most most detailed and comprehensive analysis of
World Trade Center dust
had been published by a group of independent researchers
including physicist Steven P. Jones and chemist Kevin Ryan.
Combining data from earlier published studies
with results from experiments on dust samples they had obtained,
these scientists found both
the apparent
products of aluminothermic pyrotechnics
and
unexploded fragments of such pyrotechnics.
These researchers also examined published data on the
emissions of gases
from Gound Zero,
and supplied straightforward hypotheses,
consistent with the view that
energetic materials were used to destroy the complex,
for observations that were highly anomalous
within the context of the government-sanctioned collapse theory.